Ionic liquids Toxic or not?


1. Biorenewables and Bioprocessing Group, Process and Environmental Research Division, University of Nottingham, Department of Chemical and Environmental Engineering, University Park, Nottingham NG7 2RD, UK
2. University of Nottingham, School of Chemistry, University Park, Nottingham NG7 2RD, UK


Ionic liquids received a bad press in the early days when it was discovered that imidazolium and pyridinium salts with long alkyl substituents were extremely toxic. Now that ionic liquid structure-activity relationships are better understood, it is possible to design new, task-specific ionic liquids to span the entire toxicity range, from biocides right through to non-toxic, environmentally benign ionic liquids. Thus, there is nothing special about ionic liquid toxicology: just like any other group of chemicals, some are toxic and some are not


Until very recently, imidazolium derivatives had rarely found application either as building blocks or commercial products (1), so there had been little previous incentive to study their toxicology or even their broader impact in our environment. In the 1990s, it was realised that ionic liquids represented a “Green” alternative to conventional, more volatile, molecular solvents (2). This prompted an explosion of research effort at record breaking pace and with unprecedented productivity, based on the application of archetypical 1,3-dialkylimidazolium-based salts (2, 3). Consequently, the “new” ionic liquids represented “virgin territory” for toxicity studies, and they immediately began to capture the attention of the ecotoxicology research community.
The immediate target was to develop Quantitative Structure Activity Relationships (QSAR), beginning with simple homologous series of 1,3-dialkylimidazolium-based halides with increasing alkyl chain lengths. On inspection it was clear that, as the chain length increased, the salts became more toxic. It was also apparent that there was a strong cor ...